Radio frequency heating apparatus



g- 1969 J. a. D. MANWARING 3,461,263

RADIO FREQUENCY HEATING APPARATUS Filed July 31, 1967 United StatesPatent 3,461,263 RADIO FREQUENCY HEATING APPARATUS Joshua G. D.Manwaring, Needham, Mass., assignor to Radio Frequency Co., Inc.,Medfield, Mass., a corporation of Massachusetts Filed July 31, 1967,Ser. No. 657,294 Int. Cl. H051) 9/04, 9/06, 5/00 US. Cl. 21910.81 4Claims ABSTRACT OF THE DISCLOSURE This invention relates to radiofrequency circuitry and components and, more particularly, to radiofrequency heating equipment and electrode systems useful therein.

It is a primary object of the present invention to propide an improved,compact, relatively simple and inexpensive, easily cleaned stray fieldelectrode system which can be used for either single or double surfaceradio frequency heating. Other objects include providing an electrodesystem which is of simple and rugged construction and which may bereadily tuned to accommodate a variety of conditions.

The invention accomplishes these and other objects by providing a strayfield electrode system comprising a pair of spaced coplanar conductiveplates and a plurality of parallel, conductive electrode elementsalternately arranged in two series extending transversely of the plates.Each electrode element of one series comprises a sheet metal membermounted on the first plate electrode and with an edge surface of themember parallel thereto. Each electrode element of the second series issecured to the second plate electrode and includes a rod portionextending transverse, parallel and adjustable relative to the secondplate electrode. In preferred embodiments the electrode elements of thesecond series comprise rods having base portions parallel to and legportions perpendicular and secured to the second plate electrode, andhairpin tuning loops of conductive sheet metal electrically connect theplate electrodes.

The electrode system provided by the present invention is particularlyuseful in combination with radio frequency heating apparatus of the typedisclosed in my application Ser. No. 570,780, filed Aug. 8, 1966, newPatent No. 3,329,796 dated July 4, 1967, which utilizes a tuned loadcircuit comprising a generally tubular electrically conductiveenclosure, preferably of rectangular cross-section with a pair ofopposite ends spaced a substantial distance from one another, with aplate circuit component having its series of plates mounted within theenclosure perpendicular to its walls and extending therealong throughoutthe length of the enclosure between its open ends. The plate circuit isconnected to the enclosure and also to a radio frequency generator forheating material positioned within or without the enclosure.

Other objects, features and advantages will appear from the followingdetailed description of a preferred embodiment of the invention, takentogether with the attached drawings in which:

FIG. 1 is a perspective view of a stray field electrode constructed inaccordance with the present invention; and,

FIGS. 2 and 3 are sectional plan views of the electrode in FIG. 1.

Referring more particularly to the drawings, the stray field electrode10 here illustrated comprises two substantially parallel plateelectrodes, 12, 14 spaced one above the other and three tunabe inductivehairpin loops 16 of conductive sheet metal secured to and electricallyconnecting the plate electrodes. Each hairpin loop 16 in cludes a tuningportion 18 parallel with plate electrodes 12 and 14 and connectingportions 20 and 22 generally perpendicular to the plate electrodes andconnected, respectively, to plate electrodes 12 and 14. A shortingmember 24 is slideably mounted on the tuning portion 18 each of haidpinloops 16 for tuning.

For producing the stray field, a plurality of elongated, transverselyextending, stray field electrode elements are mounted in parallelrelationship on each of the plate electrodes on the side thereof,opposite tuning portions 18 of hairpin loops 16. The stray fieldelectrode elements are alternately arranged to form two series, series26 and series 28. Each electrode element 30 of series 26 comprises agenerally planar, conductive sheet metal element mounted on plateelectrode in position generally perpendicular and transverse thereto.The upper longitudinal edges 32 of the electrode elements 30 of series26 lie in a common plane spaced above and parallel to plate electrode12. Each electrode element of the other series, series 28, comprises asubstantial U-shaped conductive rod having a base portion 40 of each rodparallel to plate electrodes 12 and 14 and spaced thereabove and twolegs 42, 44 extending perpendicularly and secured by nuts 46 to plateelectrode 14. Legs 42 extend through openings 48 in, and legs 44 arespaced beyond the longitudinal edge of, plate electrode 12 so that noportion of the rod electrode elements of series 28 directly contactplate electrode 12. Major portions of each leg 42, 44 are threaded sothat the rod electrode elements may be adjusted relative to the plateselectrodes. A plurality of insulating support members 50 and 52 extendbetween and are secured to electrode elements 30 and plate electrode 14,and plate electrode 14 and tuning loops 16, respectively, for rigidity.

In operation, the electrode elements may be mounted with surfaces 27 ofthe sheet metal elements of series 26 and base portions 40 of the rodelements of series 28 arranged either for heating on one side of of amaterial passed over the electrodes, as shown in FIG. 2, or as shown inFIG. 3, for heating both sides of material passed between the two seriesof electrodes. For single side heating (FIG. 2) the rod elements ofseries 28 are adjusted so that base portions 40 of each rod electrodeelement lies in thep lane defined by surfaces 27 of the sheet metalelectrodes 30 of series 26. For two side material heating (FIG. 3) thebase portions 40 of the rod electrodes are adjusted upwardly by means ofnuts 46 so that base portions 40 of the rods lie in a second planesubstantially parallel with the plane of surfaces 27 of the sheet metalelectrodes but spaced thereabove. Material to be heated may be passedbetween the two planes.

Other embodiments within the scope of the following claims will occur tothose skilled in the art.

What is calimed is:

1. A stray field electrode comprising:

first and second parallel, electrically conductive plate electrodesspaced one above the other; and,

a plurality of parallel, conductive electrode elements alternatelyarranged in two series extending transversely of said plate electrodes,

each electrode of said first series being electrically connected to saidfirst plate electrode and comprising a sheet metal member mounted onsaid first plate electrode with a longitudinal edge surface of saidmember parallel thereto,

each electrode of said second series comprising a rod having a baseportion generally parallel to said second plate electrode and at leastone leg portion generally perpendicular and adjustably secured to saidsecond plate electrode.

2. A stray field electrode comprising:

first and second parallel, electrically conductive plate electrodesspaced one above the other; and

a plurality of parallel conductive electrode elements alternatelyarranged in two series extending transversely of said plate electrodes,

each electrode of said first series being electrically connected to saidfirst plate electrode and comprising a sheet metal member mounted onsaid first plate electrode with a longitudinal edge surface of saidmember parallel thereto,

each electrode of said second series being electrically connected to andincluding a rod portion parallel and adjustable relative to said secondplate electrode and said edge surfaces of said members lying in a commonplane substantially parallel with said first plate electrode and saidelectrodes of said second series being adjustable between a firstposition in which said rod portions lie in said common plane and asecond position in which said rod portions lie in a second planeparallel to and spaced from said common plane. 3. The stray fieldelectrode of claim 2 including a plurality of hairpin loops ofconductive sheet metal electrically connected to said plate electrode, ashorting member being slideably mounted on each of said hairpin loops.4. The stray field electrode of claim 3 in which each of said members issubstantially perpendicular to said first plate electrode and eachelectrode of said second series comprises a rod having a base portiongenerally parallel to said second plate electrode and two leg porti onsgenerally perpendicular and adjustably secured to said second plateelectrode.

References Cited UNITED STATES PATENTS 2,783,347 2/1957 Warren 21910.81X 2,842,650 7/1958 Naylor et al. 219-10.81 X 3,329,797 7/1967 Clark219-10.81 3,344,254 9/1967 Manraring 2l910.8l

JOSEPH V. TRUHE, Primary Examiner L. H. BENDER, Assistant Examiner U.S.Cl. X.R.

